Impact wrench



June 25, 1968 MlTsUGl KAWAMoTo 3,389,756

IMPACT WRENCH Filed Dit. 21,

5 NTI United States Patent O 3,389,756 IMPACT WRENCH Mitsugi Kawamoto, 23 Mizuhai, Kawachi-shi, Osaka-fu, Japan Filed Oct. 21, 1965, Ser. No. 499,302 Claims priority, application Japan, Aug. 9, 1965, 40/48,058 7 Claims. (Cl. 173-935) ABSTRACT F THE DISCLOSURE An impact wrench has a rotating hammer with at least one impact jaw, a rotatable anvil coaxial with and spaced from the hammer, a central shaft extending between the hammer and anvil and rotatable with the hammer and a dog surrounding the shaft between the anvil and the hammer. The dog has at least one impact jaw and is rotatable with the anvil while being movable axially between a first position in which the jaw on the dog is clear of the dog on the hammer and a second position in which the jaw on the dog is engageable with the jaw on the hammer. Spring means biases the dog to said iirst position and cam means is provided for moving the dog axially to said second position upon predetermined rotational movement of said anvil and dog relative to the hammer. The jaw on the dog is thereby brought into position for impacting by the jaw on the hammer.

The present invention relates to improvements in impact wrench in general, and more particularly to an impact wrench driven by an electric or pneumatic motor or the like, and so constructed as to provide periodic impact upon the wrench or screw driver, in the event resistance to turning increases.

In impact wrenches of this character, an anvil is dealt blows directly by rotating hammer, or by hammer dogs carried by the rotating hammer by means of intermittently bringing into engagement with the anvil to impart rotary impacting blows to the anvil. In these cases, when the load for rotation of the anvil is light, the hammer or hammer dogs which have the function to transfer the impact blows of the hammer to the anvil rotate with the anvil, or rotate independently of the anvil. And, when the resistance to turning increases, the hammer or hammer dog provide periodic impact blows to the anvil.

The principal object of the present invention is a provision of impact wrench having simple construction and durable properties and an economical construction which provide periodic impact energies upon the anvil by the rotational energy of rotating hammer which is driven by a suitable driving means of electric or pneumatic motor, in the event resistance to turning the anvil increases.

`Other objects and advantages will appear from the following description and drawings, wherein:

FIG. 1 is a side view of a motor driven impact wrench according to the present invention shown in axial section,

FIG. 2 is a sectional view taken along the line II-II of the impact wrench shown in FIG. 1,

FIG. 3 is a sectional view taken along the line IlI-III of the impact wrench shown in FIG. 1,

FIG. 4 is a sectional view taken along the line IV-IV of the impact wrench shown in FIG. 1,

FIG. 5 is a side view of the impact wrench shown in FIG. 1, under the impact condition of hammer jaws with jaws of the dog member,

FIG. 6 is a sectional view taken -along the line VI-VI in FIG. 5 and showing the relative position of hammer jaws and dog jaws and ball, under the impact condition of hammer jaws with the jaws of the dog member.

3,389,756 Patented .lune 25, 1958 ice Referring to the drawings of FIGS. 1 to 6, particularly to FIGS. 1 and 5, a housing 15 encloses an impact wrench assembly of an embodiment o-f the present invention. The housing 15 is afxed to la motor housing, which encloses a pneumatic motor. The motor means includes a shaft which projects from the motor housing. A motor shaft has a splined portion or key grooved portion `6 at its front end, which enters into a counterbore 32 formed in a hammer element 3. The hammer element 3 is supported at its rearward end by a ball bearing 30 which is mounted in the motor housing. A cam shaft 4 is rigidly secured and supported at its rear end within the bore 34 of the hammer element by a pair of roller pins 7 as shown in FIG. 4. The forward part of the cam shaft 4 slidably engages with a bore 11 formed in -an anvil 1 which is positioned for rotary motion in the forward end of the housing 15. The outer end of the anvil 1 which projects from the housing 15 forms an output shaft having a polygonal section, and the anvil 1 is rotatably supported by a sleeve 5 at the portion inside of the polygonal shaped shaft portion of the anvil 1. A ring shaped cam 42 having larger diameter compared with that of the cam shaft 4 is rigidly secured to the forward portion of the cam shaft 4 and is provided with a rearward projecting portion 43.

A hammer dog 2 is provided with coaxial bore 21, a ring shaped flange portion 23 projecting inward and a recess 22, and the bore 21 forms a guide piece having plural number of grooves 21' which extend in the axial direction and slidably engage with axial projections 12 disposed coaxially around the rearward portion of the anvil 1. However, it is understood that other means of slidable engagement of hammer dog with the anvil such as spline engagement may be satisfactory. The ring portion 23 slidably and rotatably engages with the cam shaft 4 and a cam ball 10 is supported in the space between the surface of the cam 42 and the inner wall of the recess 22 and the side wall of the flange portion 23. A compression spring 9 is disposed `around the cam shaft 4 in the space between the ring portion 23 and a collar 8 disposed at the rearward end of the bore 34 of the hammer element 3 so as to maintain the ball 10 in contact with the surface of cam 42 and the side wall of the ring portion 23 of the hammer dog 2. Therefore, the hammer dog 2 and the anvil 1 are slidably engaged in a telescoped condition within a rotating hammer element 3. The hammer dog 2 may thus rotate relative to the cam shaft 4 without advancing as this is limited by the angular extent of the recess 22 and the Hat surface of the cam 42. The angular extent of the recess 22 in the hammer dog 2 for providing the relative angular movement of the hammer dog to the cam shaft 4 is illustrated in FIG. 3.

The hammer dog 2 is provided with impact jaws 24 projecting rearwardly so las to engage with impact jaws 31 formed in a forward portion of the hammer element 3 when the hammer dog is displaced to the backward position by means of the action of cam 42, when the resistance to turning of the anvil increases.

It will be observed that as long as the ball 10 is carried rotationally with respect to the cam shaft 4 and rides along the fiat portion of the cam 42, the jaws on the hammer dog 2 will be in a retracted position with respect to the path of the jaws 31 of the hammer element 3. When, however, the ball 10 is carried along the cam 42 and up the rearward projection 43, the hammer dog 2 is displaced axially so that the jaws of the hammer dog 2 are positioned in the space between the rotating jaws of the hammer element 3. The axial movement of the ball 10 along the cam surface of the cam 42 is provided by the increase in resistance to turning of the anvil 1. When the turning resistance of the anvil 1 increases, the axial component of the torque on the cam portion 42 which is provided by the force transferred through the anvil 1 and the hammer dog 2 will correspondingly increase, until it is sufficient to overcome the expansion force of the spring 9. Thereupon, when the torque overcomes the force of the compressed spring 9, the ball 10 rides over the rearward projecting portion 43 of the cam 42, thereby momentarily terminating the cam engagement and causing an initial impact of the jaws 24 of the hammer dog with the impact jaws 31 of the hammer element 3 and then the impact force is transferred to the anvil 1 through the sliding engagement of the hammer dog with the anvil, as shown in FIG. and FIG. 6.

After the impact engagement of the hammer dog 2 with the hammer element 3 is made, the hammer dog Z is displaced forward by the -force of the spring 9. During the abrupt increase in resistance to rotation, the hammer element 3 is decelerated and after the ball 10 passes over the rearward projection 43 of the cam 42, the hammer element is accelerated for almost one full revolution before the ball re-engages cam surface 43. During such rearward movement, the ball 10 engages the bac-k slope of the projection 43 of the cam 42 thereby rotating the cam shaft 4 slightly' so as to provide a phase difierence between the hammer dog 2 and the cam shaft 4, therefore the cam surface does not interfere with the forward movement of the hammer dog along the cam shaft. Such slight rotational movement of the hammer dog 2 against the cam shaft 4 is possible because of the arrangement of the ball 10 and the recess 22 shown in FIG. 3 and FIG. 6, and it prevents interference with forward movement of the hammer dog 2.

It is intended, therefore, that all matters contained in the foregoing description and in the drawings shall be interpreted as illustrative only and not as limitative of the invention.

What is claimed is:

1. An impact wrench comprising in combination, a easing, a rotatable hammer having `at least one impact jaw, bearing means supporting said hammer for rotation Without axial movement, drive means for rotating said hammer, a rotatable anvil coaxial with and axially spaced from said hammer, bearing means supporting said anvil for rotation without axial movement, a central shaft extending between said hammer and anvil, said shaft being fixed relative to said hammer and rotatable relative to said anvil, an annular dog surrounding said shaft between said hammer and anvil, means connecting said dog with said anvil Ifor rotation therewith and for axial movement relative thereto, said dog having at least one impact jaw adapted to be engaged by said impact jaw of said hammer and being movable axially between a first position in which said impact jaw of said dog is clear of said irnpact jaw of said hammer and a second position in which said impact jaw of said dog is in position to be engaged by said impact jaw of the hammer, spring means acting between said dog and hammer to bias said dog normally to said first position and cam means acting between said shaft and said dog upon relative predetermined rotational movement between said hammer and anvil to move said dog axially from said first to said second position for impacting of said jaw on said dog by said jaw on said hammer.

2. An impact wrench according to claim 1, in which a portion of said anvil is received in a recess in said dog, and in which said means connecting said dog with said anvil comprises axially extending projections on the periphery of said anvil portion received in axially extending grooves in said dog recess receiving said anvil portion.

3. An impact wrench according to claim 1, in which said spring means comprises a spiral spring surrounding said shaft and having an end portion received in a recess in said hammer and an opposite end portion engaging said dog.

4. An impact wrench according to claim 1, in which said spring means is of sufficient strength to cause said dog and anvil to rotate with said hammer until a predetermined torque load is imposed on said anvil and thereupon to permit relative rotational movement of Said dog and anvil relative to said hammer.

5. An impact wrench according to claim 1, in which said means for moving said dog axially against said spring means comprises an annular cam on said shaft and a ball between said cam and said dog.

6. An impact wrench according to claim 5 in which said cam has a circular portion and a portion projecting toward said hammer and in which said dog has a recess receiving said ball and providing limited circumferential j movement of said ball relative to said dog, whereby said ball upon passing up one side and over the extremity of said projecting portion of said cam can ride down the other side.

7. An impact wrench according to claim 5, in which said dog has an inner liange portion slidably engaging said shaft, and in which said spring means engages one side of said flange portion while said ball engages the opposite side.

References Cited UNITED STATES PATENTS t 2,373,666 4/1945 Emery 173-936 2,747,447 5/1956 Burleigh 173-936 2,825,436 3/1958 Amtsberg 173-936 3,053,360 9/1962 Madsen 173-93.6 3,208,568 -9/1965 Vaughn 173-93 DAVID H. BROWN, Primary Examiner'.

CHARLES E. OCONNELL, Examiner. 

